This invention relates to electrical arc welding and more particularly to mechanisms for maintaining a uniform height of deposit of weld material along a seam.
Arc welding is used in the manufacture of diverse different products to join workpieces which are to become an integral element. Typically, the parts to be joined are supported in a welding fixture and a small gap or groove is left therebetween which is to be filled by material melted from a consumable welding electrode or wire by establishing an electrical arc between the electrode and the workpiece. While the adjacent edges of the parts to be joined are shaped, prior to installation in the welding fixture, to establish a weld groove of desired configuration and uniformity, manufacturing tolerances may result in some variation of the actual width of this groove along its length.
The welding head carrying the consumable electrode is moved along the groove, while the electrical arc is present, in order to cause the melting and depositing of material. If the motion of the welding head along the groove, the rate of feeding of the electrode material and the voltage applied between the welding head and workpiece all remain constant, then irregularity in the shape of the groove may cause an unevenness in the height of the weld material which is deposited along the groove. As a consequence, portions of the weld groove may be overfilled while others are underfilled. This has several undesirable effects such as an unevenness in the strength of the weld at various points in the seam and a wastage of welding material. To correct for the problem, costly additional supplementary welding to add material or grinding of the welded part to remove excessive material may be needed.
One known technique for avoiding or at least reducing this problem is simply to have an operator carefully observe the progress of the weld while operating a control which enables him to adjust the amount of material deposited at each stage as might be necessary. This is undesirable in that it generally requires the operator to give his undivided attention to a single welding operation and thereby greatly restricts his productivity. Further, it is not an entirely satisfactory procedure in practice as great difficulty may be encountered in maintaining a uniform welding bead simply by visual observation and manual adjustment of controls.
Accordingly, various systems have heretofore been developed to sense deviation of weld depth from the desired value and to make an automatic corrective adjustment of some parameter of the apparatus. The sensing means have typically included such devices as infrared sensitive devices or photoelectric elements or mechanical probes which ride along the weld groove. In order to make the compensating adjustments in response to the output of the sensing means, the prior systems variously change the rate of feed of electrode material, adjust the height of the welding head above the workpiece, vary the travel of the welding head relative to the workpiece or vary the arc current. Such systems either require costly and complex additions to the basic welding apparatus or else involve the usage of sensing means which are fragile and prone to malfunction or which must physically contact the thermally corrosive environment of the melt pool.
In many cases substantial system complication is also necessary to avoid malfunction in the event that the volume of melted weld material which is being monitored should be lost because of the proximity of an edge of the workpiece being welded or because of passage of the arc across an opening in the workpiece or for some other reason. Under these circumstances the sensors emit a signal which is normally indicative of a decrease in the weld height from the desired norm. In the absence of complex corrective means, the automatic system may then respond with a compensatory increase in the rate of electrode feed or some other parameter which is not in fact needed under the circumstances.